Another character he could interact with is Thor. Thor's otherworldly nature and his powerful abilities would be quite a contrast to Stiles. Maybe Stiles could help Thor understand some earthly concepts while Thor could teach Stiles about Asgardian culture and power.
One possible plot could be that Stiles is a huge Avengers fan in his own world, and through some magical or scientific mishap, he gets to meet his heroes. But it's not all fun and games. He has to prove himself worthy of being part of their team. He could also bring in some of his own world's technology or ideas that help the Avengers face a new and powerful threat.
One good Stiles - Avenger crossover is 'Stiles in the Marvel Universe'. It has an interesting plot where Stiles uses his wits from the Teen Wolf world to interact with the Avengers. Another is 'Stiles and the Avengers: An Unexpected Alliance' which shows how Stiles' unique skills could be useful to the Avengers.
He might also interact with characters that are no longer alive in his present time. For example, an older werewolf or a witch who was powerful in the past. These interactions could provide Stiles with valuable knowledge or magic that he can use to his advantage when he returns to his own time. It could also create some really cool action scenes and moments of discovery as he uncovers secrets long forgotten.
It could be his love interest, like I mentioned before, Lydia. She might reject him because she's too focused on her own goals or perhaps she doesn't see Stiles in that way at the time. Their relationship has always been a bit complex in the show, so this would be a likely scenario in fanfiction.
His best friend could discover it. Since they are so close, they might notice something different about Stiles that makes them suspect he's actually a girl.
A kind stranger could come to his aid. Maybe someone who has been through a similar situation in the past. This person could offer practical advice on how to survive while being on the run and pregnant. They might also teach Stiles some skills like cooking healthy meals for the baby's sake.
It could be a rogue werewolf. Maybe this werewolf has a grudge against Stiles' pack and thinks that by kidnapping Stiles, he can get some sort of revenge or leverage.
Stiles' father could be a major character. He would be worried sick about his son and use all his resources to try and find him. Maybe he teams up with some of Stiles' friends like Scott or Lydia.
In Stiles werewolf fanfiction, Stiles is often depicted as intelligent. He uses his smarts to navigate the complex world of werewolves. For example, he might figure out a way to break a werewolf curse using his knowledge.
There could be a tough drill sergeant who acts as a mentor and a source of conflict for Stiles. This character would be strict but fair, and would push Stiles to his limits.